The fusing roller in electrostatographic copiers and printers is a commonly replaced and expensive component. It is generally replaced by a serviceman who must connect the roller to various cooperating parts, including structure for applying offset-preventing liquid (sometimes called "fusing oil") to it.
U.S. Pat. No. 4,899,197 shows an electrophotographic apparatus in which a color toner image is formed on a receiving sheet. The image is fused by a conventional roller fuser having a heated fusing roller and an unheated pressure roller urged together. The reference discusses at length the problems of servicing the fuser, including substantial problems associated with wear to the fusing roller. Servicing in this prior apparatus is facilitated by a fusing oil-applying mechanism that is replaceable in its own cartridge. The nip between the rollers is made accessible for servicing and for clearing jams by locating the upper pressure roller in an upper portion of the image-forming apparatus that is pivotable away from a lower portion containing the lower roller.
Japanese Patent Application 63-107319 (1988), laid-open Nov. 7, 1989 (1-277271), shows a fuser in which a large portion of the entire fuser is replaceable in a single unit. Most fusing oil-applying structure in this reference is permanent and must be coupled to the fusing roller with replacement of the unit.
Application of fusing oil to the fusing roller in prior structures has been accomplished with a variety of mechanisms. For example, oil can be applied by a stationary wick which has one end in a reservoir and the other end contacting the fusing roller. The wick can be made movable for control of oil application. Another common structure includes an articulatable roller to which oil is applied by an external wick.
U.S. Pat. No. 4,429,990, granted to E. J. Tamary Feb. 7, 1984, discloses a wicking structure in which oil is transported under pressure from a container to a permanent internal feed tube located inside a replaceable porous applicating wick. At least the outside portion of the wick is rotatable by the roller being oiled. For other examples of rotating wicks, see U.S. Pat. Nos. 4,908,670; 5,043,768; and 3,964,431.
To control the amount of oil in most prior wicking devices, either the rotating wick, roller or stationary wick is articulatable into and out of contact with either the surface being oiled or a surface further upstream. It is also possible to control wicking by controlling a pump feeding oil to the system.